The problem of corrosion of non-metallic inorganic items, such as glassware, ceramic and enamel materials, when subjected to automatic dishwashing processes is well recognised in the art. For example, it has been proposed that the problem of glassware corrosion is the result of two separate phenomena. Firstly, it is suggested that the corrosion is due to leakage of minerals from the glass network, accompanied by hydrolysis of the silicate network. Secondly, silicate material is suggested to be released from the glass.
These phenomena can cause damage to glassware after a number of separate wash cycles. The damage may include cloudiness, scratches, streaks and other discoloration/detrimental effects.
Silicate materials have been suggested to be effective in preventing materials from being released by the glass composition. However, the use of silicate compounds can have detrimental side effects, such as the tendency to increase separation of silicate material at the glass surface.
A further solution has been to use zinc, either in metallic form (such as described in U.S. Pat. No. 3,677,820) or in the form of compounds. The use of soluble zinc compounds in the prevention of glassware corrosion in a dishwasher is described in, for example, U.S. Pat. No. 3,255,117.
However, the use of soluble zinc compounds can give rise to detrimental side effects, such as the development of a precipitate of insoluble zinc compounds formed by interaction with other species typically present in the dishwasher wash liquor. This has meant that often insoluble (or rather sparingly soluble) zinc compounds are preferred as the source of zinc in the dishwasher wash liquor. European Patents; EP-A-0 383 480, EP-A-0 383 482 and EP-A-0 387 997) describe the use of water insoluble compounds including zinc silicate, zinc carbonate, basic zinc carbonate (Zn2(OH)2CO3), zinc hydroxide, zinc oxalate, zinc monophosphate (Zn3(PO4)2) and zinc pyrophosphate (Zn2P2O7) for this purpose.
As these zinc compounds have only a low solubility in water it is usual that the compounds are required to have a relatively high surface area, achieved by having a small particle size, in order to attempt to achieve a sufficient concentration in water to obtain the required glass corrosion prevention effect. In this regard EP-A-0 383 480 and EP-A-0 387 997 specify that the zinc compound should have a particle size of lower that 250 μm, whereas EP-A-0 383 482 specifies a particle size of lower than 1.7 mm. However, the use of a small particle size has not been found to overcome the delivery issue and thus, with the use of these insoluble compounds, the problem of glass corrosion effects remain.
The use of glasses and ceramics containing zinc has been found to address the problem of glassware corrosion in a dishwasher. WO-A-01/64823 describes the use of a ceramic composition comprising zinc to protect glassware in an automatic dishwashing process. GB-A-2 372 500 and WO-A-00/39259 describe the use of a soluble glass composition comprising zinc (present in the form of ions) to protect glassware in an automatic dishwashing process. The use of a ceramic/glass zinc containing composition overcomes the problems of poor solubility/precipitation described above whilst offering effective glassware protection.
Bismuth has been used as an additive to aid the prevention of corrosion of glazed glassware corrosion. For example, BE 860180 describes the use of bismuth to avoid damage of decorated, glazed articles.
However, the value of bismuth in this purpose has been diminished by the detrimental effects that the use of bismuth compound has on other components of the washing process or detergent composition. In soluble bismuth compounds can cause the formation of stains on kitchenware items e.g. glassware and cutlery which come into contact with these compounds. For these reasons the use of bismuth alone as a glaze protector has been avoided, although a combination of zinc and bismuth has been found to address this issue (see WO-A-04/106476).
It has also been found that the use of heavy metal compounds in some circumstances reduce the bleaching performance of a dishwashing composition on bleachable stains such as tea stains.
Furthermore, for environmental reasons, it is becoming increasingly desirable to limit (and especially to avoid) the use of heavy metals in detergent formulations.
Moreover, when insoluble materials are incorporated into compositions it is generally necessary to use them in their solid form. As suggested above, this can require careful control of the particle size of the material and can also make them awkward to use in a factory environment as problems such as release of a dust containing the material may occur. It is therefore frequently desirable to use raw materials which are soluble/in liquid form.
A further problem is that the known corrosion prevention agents for non-metallic surfaces, such as glassware corrosion agents, are only effective in the dishwashing cycle in which they are used. Thus if the consumer does not ensure that a composition comprising these agents is used in each cycle then protection against corrosion of non-metallic items is not obtained in each cycle.
Yet another problem some known types of corrosion prevention agents, e.g. zinc containing agent, is they suffer from reduced efficacy in detergent formulations which comprise builders with a strong complexing action such as phosphates and aminocarboxylates.
Still a further problem is that some of the known corrosion prevention agents, such as bismuth containing agents, are in relatively short supply. Accordingly there is always a need to find alternative materials which are more readily available and/or less expensive.
It is an object of the present invention to address one or more of the above problems.
In particular, it is an object of the present invention to provide a corrosion prevention agent/composition which reduces, or avoids, detrimental effects on items treated therewith, e.g. which does not stain such items.
It is a further object of the present invention to provide a corrosion prevention agent/composition which reduces, or avoids, detrimental effects on either i) the other ingredients in the composition into which it is incorporated or ii) which is compatible with strongly complexing builders such as phosphates and aminocarboxylates.
It is still a further object, for environmental reasons, to provide a corrosion prevention agent/composition which does not contain heavy metals, which agent is to be used on non-metallic inorganic items.
Another object is to provide a corrosion prevention agent/composition for non-metallic inorganic items which is readily soluble in water and/or can be provided in liquid or gel form.
Still a further object of the present invention is to provide a corrosion prevention agent/composition for non-metallic inorganic items which agent provides the prevention effect even if it is not used in each cycle of the dishwasher or every time the dishwasher is operated.
Another object of the present invention is to provide a corrosion prevention/composition agent for non-metallic non-inorganic items which is readily available and/or relatively inexpensive compared to such currently available corrosion protection agents.